In recent years, fiber-reinforced molded resin articles comprising a glass fiber fabric as a reinforcing material and comprising an epoxy resin or the like as a matrix resin have been widely used for printed boards, transparent sheet materials, and the like. Recently, with the miniaturization and weight reduction of electronic equipment, the requirement of the thinning of fiber-reinforced molded resin articles has become strong. For the thinning of fiber-reinforced molded resin articles, it is preferable to use a glass fiber fabric in which mass is small and thickness is thin, and it is preferable to uniformly dispose a glass fiber fabric in which weaving yarns (filaments) of glass fibers are widened, in a fiber-reinforced molded resin article and smooth it. Further, in order to further increase the CAF (Conductive Anodic Filament) resistance of printed boards, the transparency of transparent sheets, and the like, a further improvement in the resin impregnation property of glass fiber fabrics is required.
Therefore, conventionally, it has been considered that a fiber-opening treatment for glass fiber fabrics and the provision of silica microparticles to glass fiber fabrics are performed in order to improve the smoothness and resin impregnation property of the glass fiber fabrics. For example, a process of removing a sizing agent attached on glass fibers by a heat treatment, then immersing a glass fiber fabric in an aqueous dispersion of silica microparticles to provide a surface treatment, and then providing a fiber-opening treatment is described in Patent Literature 1. In addition, a process of removing a sizing agent attached on glass fibers by a heat treatment and then providing a fiber-opening treatment to a glass fiber fabric in an aqueous dispersion of silica microparticles is described in Patent Literature 2. By attaching silica microparticles on a glass fiber fabric using the processes described in Patent Literature 1 and Patent Literature 2, in this manner, certain resin impregnation property can be improved.